Recently developed methods for in vitro culture of rat trophoblast will be used to establish predictable structure-function relationships related to the development and differentiation of trophoblast. We will examine if these processes are regulated or occur autonomously. Rat trophectoderm attaches to endometrium and insinuates itself between epithelial cells. Trophoplast penetrates decidualized stroma by an invasive process to establish a relationship with maternal vasculature. Blastocysts cultured in vitro follow a similar pattern and provide a productive model for studying trophoblast development in experimentally alterable defined conditions. We propose to characterize trophoblast differentiation by analyzing specific developmental landmarks. Morphogenesis and trophoblast outgrowth (cytodifferentiation, microtubule assembly) will be correlated with indices of invasiveness (plasmingen activator) and biochemical differentiation (steroid and peptide hormone synthesis). Co-culture experiments with monolayers of individual endometrial cell types will indicate the influence of cell communication (cell-cell, cell-extracellular matrix) on the course of normal and abnormal trophoblast development. The use of developmental landmarks, feasible because of in vitro culture, provides for new insights relative to structure-function correlates of trophoblast development.